SEATTLE (CBS/AP) Surveillance cameras captured the brutal beating of a 15-year-old girl in a downtown Seattle bus tunnel while three security guards watched without ever intervening.

The guards' actions during the Jan. 28 brutal attack prompted an outcry from Metro Transit and King County authorities, who said they wished the guards had broken up the fight even though they were just following orders not to interfere.

Police arrived minutes after the attack, and after the group had fled. Police tracked down four suspects, including the alleged attacker, another 15-year-old girl, and arrested them on Friday and Saturday. All four were charged with first-degree robbery for theft of a purse, phone, and iPod.

In court papers filed Wednesday, the victim told authorities she deliberately stood next to the three guards and thought they would protect her.

Surveillance video first aired by Seattle's KING-TV this week shows the attack at Westlake Station on Jan. 28. The victim appears several seconds before her attackers and sidles up to the three guards, who are standing together and talking.

A teen girl shoves the victim and begins punching her. The two crash into a wall and then onto the floor. The assailant gets up and kicks and stomps on the girl's head. Others grab her possessions.

(CBS)

The guards, who have standing orders to "observe and report," called police.

The 15-year-old victim, who reported that she lost consciousness during the attack, was not hospitalized but did see a doctor.

King County Sheriff's Sgt. John Urquhart said the guards were right to follow their training.

"If you're a bank teller and you do something other than give them the money, you're going to get fired," Urquhart said. "We don't expect civilians to take police action. In this case, it was a violent fight, and they were outnumbered by this pack of people 3-to-1."